The Impact of new Web Service Standards for Resources, Events and Management within OMII-UK.

Malcolm Atkinson, David de Roure, Carole Goble, Steven Newhouse (May 2006)

Summary

The recent announcement by IBM, HP and Microsoft to converge web services management standards will have a direct impact on the long-term future of Web Services Resource Framework (WSRF) used by projects within OMII-UK and the wider Grid community. The on-the-wire protocols and interfaces used by WSRF services will change if projects migrate to the new standards as they become supported in 18-24 months time. This migration should just be a simple re-factoring as many of the concepts contained within WSRF will be supported in the new standards.

OMII-UK will continue to explore the WSRF approach as means of better informing the development and adoption of the new management standards, while investing in implementations of the specifications that will form the basis of these new standards. To protect our user and application development community, we will also continue our investment in defining and standardising (through the relevant bodies) programming interfaces that are neutral to the underlying protocols. These interfaces will allow our community to use our current services, and migrate to new versions of these services, built on top of these new specifications, with minimal changes to their current applications.

Background

Over the last 5 years web services have formed the basis of many grid middleware activities and have been successfully adopted within many e-Science projects. Two approaches have proved successful: the use of off-the-shelf web service specifications, and specifications developed to meet the specific use cases from the grid computing and e Science community initially OGSI (the Open Grid Services Infrastructure) and more recently the WSRF (Web Services Resource Framework). The absence of committed support by all of the major industrial web service players to a single approach has led to a degree of risk in adopting one approach over the other.

Recently, the major developers of web service specifications have agreed and published a strategy that will lead to convergence of these two approaches http://devresource.hp.com/drc/specifications/wsm/index.jsp. Service developers that have used both approaches will eventually have to consider moving to the new family of specifications once they have been fully standardised - which should be in approximately 18-24 months. The composed capability of the current WS-Transfer and WS-Enumeration specifications will be extended with the new WS-Transfer Addendum, WS-ResourceTransfer, and a revised WS-MetadataExchange specification. The WS-Eventing specification will be extended with a new WS-EventNotification specification that brings in concepts currently supported in WS-Notification. These specifications provide two basic concepts - information distribution and event notification - which can not only be used to support grid computing and e-Science, but will be used to form a web services based distributed management infrastructure.

OMII-UK currently has projects that uses established web service specifications and those within the WSRF family of specifications. The services being developed within these projects will need to be re-factored to support the new converged specification set once they have been defined. It is envisaged that this will currently take place in 18-24 months time. At this point application developers who have built directly on the service interface will have to consider re-factoring their interaction with these services. We expect this process to be mechanical in nature as many of the concepts are shared between the different approaches.

OMII-UK will continue its strategy of protecting end-users and application developers investment in building upon our software distribution by:

• Providing a defined migration route to the converged specification sets when it is appropriate to do so,
• Investing in defined stable APIs that are agnostic to the specifications being used in the underlying middleware, and potentially the middleware itself,
• Providing high-level tools for end-users that interact directly with the revised services.

Through its managed programme partners, OMII-UK is investing in this strategy which it will develop over the coming months. Within the Global Grid Forum it is contributing to the Simple APIs for Grid Applications Working Group (SAGA-WG) that is defining middleware agnostic interfaces for application developers, and providing a reference implementation of this interface that will utilise the GridSAM service. Our implementation of the WS-Eventing specification in the FINS project has an interface that can be used to access similar functionality in both WS-Eventing and WS-Notification specifications. OGSA-DAI has a client-side developers library that has the same Java API to contact both the WS-RF and WS-I variants of the service. Through the Taverna workbench in the myGrid project users are abstracted from the service implementation details.

We expect to continue our investment in these areas and to expand the supported APIs and tooling in response to user demand. Likewise, we will work with the middleware developers and standards development organisations to promote application portability between different middleware stacks by defining both client and service development APIs, and common command line tools. This strategy will enable consumers of our middleware and services to be able to work with current and future versions of the OMII distribution with minimal disruption as they move between different releases.